A while back on this blog, I spent a bit of time exploring how some herbicides kill plants.
The focus was primarily on auxin-based herbicides such as 2,4-D (one of the herbicides in the notorious Agent Orange) and glyphosate, commonly known as Roundup®. The former kills primarily broadleaf plants, and the latter basically kills all plants.
In these discussions, I briefly mentioned the topic of so-called “superweeds”, which have developed a natural resistance to Roundup®. Most agree that this is a consequence of a large increase in the use of this herbicide in the past 15 years mainly because of the widespread cultivation of genetically-modified (GM) soybeans, alfalfa, corn, cotton, canola, and sugarbeets resistant to Roundup®, a.k.a., Roundup-Ready® crop plants.
In the years since I wrote these blog posts, these superweeds have become even more of a problem.
In response, farmers and ranchers are turning back to killing weeds with the old auxin-based herbicides such as 2,4-D and dicamba, which have been used for nearly 50 years. (These herbicides are the active ingredients in such products as “Weed B Gon®” that have been used for many years mainly to kill dandelions on lawns.)
Some seed and agrichemical companies are also responding to the new Roundup®-resistant superweeds by developing new GM cultivars of crop plants such as soybean and corn that can tolerate relatively high levels of 2,4-D and dicamba. (These GM plants contain bacterial enzymes that break down these herbicides.)
If these new herbicide-resistant GM crops are widely adopted, then the old auxin-based herbicides will likely be used much more heavily over vastly expanded areas of the US.
Here Comes “Agent Orange Corn” (Or Not).
The New York Times article chiefly discussed the opposition to the application to the USDA by Dow Chemical for approval of their 2,4-D resistant corn cultivars called Enlist®.
(Detractors have deemed this so-called “Agent Orange corn” because, as mentioned above, 2,4-D was one of the components of this defoliant used in the Vietnam War. This moniker is somewhat inaccurate because the other auxin-based herbicide 2,4,5-T used in Agent Orange was the more toxic of the two. Indeed, the EPA has recently ruled that 2,4-D is not seriously toxic.)
Enlist® corn is opposed not only by environmentalists concerned with potential health risks of 2,4-D, but also by farmers concerned with the deleterious “drift effects” of auxin-based herbicides. Drift effects happen when these herbicides sprayed on one field drift through the air into adjacent fields harming susceptible crop plants such as sugar beets, sunflowers, soybeans, and fruit trees.
Despite the opposition, it looks as though these new herbicide resistant GM plants will likely be officially approved by the government.
Perhaps the best argument against the adoption and widespread use of these new herbicide resistant GM crops (HRGMC) is evolution.
As pointed out in an excellent article in the January 2012 issue of Bioscience (see Ref. 1 below), greatly increased use of auxin-based herbicides anticipated as result of the widespread adoption of HMGMC’s will have intense evolutionary selection pressure on weeds. This, as with the glyphosate-resistant superweeds, will probably lead to the emergence of new generation of superweeds resistant to 2,4-D, dicamba, or both. Indeed, we may even see the emergence of super superweeds that resist not only these auxin-based herbicides but also Roundup®. Woo hoo!
As also described by the authors of Ref. 1, there are at least two other reasons to oppose this new generation of HRGMC’s. The first is the degradation of environmental quality due to a large increase in the total amount of herbicide used to manage weed control in this country. Secondly, by relying so heavily on herbicides to control weeds as a short-term fix will negatively affect smarter solutions to the problem, namely, integrated weed management (IWM).
IWM “… is characterized by reliance on multiple weed management approaches that are firmly underpinned by ecological principles.” (from Ref. 1 below)
Update: Are professional weed scientists choosing to ignore true integrated solutions to the herbicide resistance problem? (Please see Ref. 2 below for an answer to this question.)
Bottom Line: Despite the opposition, we’re probably going to see a new generation of HRGMC’s in the not-too-distant future, instead of more IWM. Seems to me this is a really bad way to go.
1. Mortensen, D. A., J. F. Egan, B. D. Maxwell, M. R. Ryan, and R. G. Smith (2012) “Navigating a critical juncture for sustainable weed management.” Bioscience, Vol. 62, pp. 75–84. (Full Text)
2. Harker, K. N., J. T. O’Donovan, R. E. Blackshaw, H. J. Beckie, C. Mallory-Smith, and B. D. Maxwell (2012) “Our View.” Weed Science, Vol. 60, pp. 143-144. (Full Text)
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